|Year : 2018 | Volume
| Issue : 2 | Page : 141-147
Effect of strabismus surgery on refractive power of the eye
Hanan S Hegazy, Nashwa M Lamie, Rasha H Abd El Salam
Department of Ophthalmology, Faculty of Medicine (for Girls), Al-Azhar University, Cairo, Egypt
|Date of Submission||13-May-2018|
|Date of Acceptance||08-Oct-2018|
|Date of Web Publication||27-Feb-2019|
Hanan S Hegazy
Department of Ophthalmology, Faculty of Medicine, (for Girls), Al-Azhar University, Nasr City 11754, Cairo
Source of Support: None, Conflict of Interest: None
Background The aim was to evaluate the refractive and corneal topographic changes occurring in the eyes after horizontal rectus muscle surgery, either unilateral recess–resect procedure or bilateral rectus muscle recession.
Patients and methods A total of 31 eyes of 20 patients were included in this study. The patients underwent strabismus surgery for concomitant horizontal strabismus (exotropia). The patients were divided into two groups. Group A included nine patients (nine eyes), who were subjected to lateral rectus muscle recession and medial rectus resection in the same eye (R&R group). Group B included 11 patients (22 eyes) who were subjected to lateral rectus recession in both eyes (bilateral lateral rectus recession group). A full ophthalmic examination including cycloplegic automated refraction was carried out. Refraction and keratometry were assessed at 1–2 weeks preoperatively and 1 week, 1 month, and 3 months postoperatively. Corneal topography was performed before and 3 months after the operation. Preoperative and postoperative refraction was compared in terms of spherical equivalent (SE) and cylindrical power.
Results The SE showed a transient statistically insignificant change toward the myopic side in the first week in both groups; these changes persisted for 2 months postoperatively and stabilized at the third month. However, the difference in SE from the preoperative values was statistically insignificant in both groups. Also, the changes in the refractive status that occurred when two muscles were operated in the same eye (R&R group) were greater than when only one muscle was operated.
Conclusion Refractive status changed postoperatively, but this change was small and reversible.
Keywords: horizontal muscle surgery, strabismus surgery, surgical induced refractive error
|How to cite this article:|
Hegazy HS, Lamie NM, Abd El Salam RH. Effect of strabismus surgery on refractive power of the eye. Al-Azhar Assiut Med J 2018;16:141-7
|How to cite this URL:|
Hegazy HS, Lamie NM, Abd El Salam RH. Effect of strabismus surgery on refractive power of the eye. Al-Azhar Assiut Med J [serial online] 2018 [cited 2020 Jul 9];16:141-7. Available from: http://www.azmj.eg.net/text.asp?2018/16/2/141/253088
| Introduction|| |
Strabismus is a misalignment of the eyes. It is a significant problem both in pediatric and in adult age groups because of its visual disability and cosmetic disfigurement. Strabismus surgery is considered to be a reconstructive rather than a cosmetic surgery. However, despite the best surgical outcome, binocular sensory motor co-ordination may not be achieved if refractive status is ignored postoperatively . Therefore, refraction should be repeated postoperatively. The effects of strabismus surgery on the refractive power of the eye have been reported in the literature ,,,,,,,,. Differences between the results of researchers have been found. Some observed significant permanent changes after strabismus surgery ,,,,. Others observed that these changes were transient and reversible ,,. Some of these discrepancies may be attributed to methodological difficulties in representing refractive power changes . The causes of refractive power changes after strabismus surgeries remain unclear. The effect of muscle tension on corneal topography is believed to be the most important mechanism of these changes ,.
| Patients and methods|| |
This prospective interventional study was carried out at the Department of Ophthalmology, Al-Zharaa University Hospital, in the period between February 2016 and December 2016. A total of 31 eyes of 20 patients were included in this study. The protocol study adhered to the tenets of the declaration of Helsenki and was approved by the Ethical Board of AL-Azhar University. An informed written consent was obtained from each participant in this study. In the case of children, consent was obtained from the parents. All surgeries were performed by the same surgeon under similar clinical and surgical settings.
Patients with strabismus ranging in age from 6 to 65 years with normal and clear ocular media and normal posterior segment were included.
Patients with a history of glaucoma, previous intraocular or strabismus surgery, extraocular muscle paralysis, nystagmus, corneal or lens opacities, macular lesions, and systemic or ocular congenital anomalies were excluded.
All patients were subjected to the following before surgery: assessment of history including age, history of strabismus or any previous eye surgeries, and best-corrected visual acuity (BCVA) determination using the Snellen’s chart. All refractions were measured by an autorefractometer using NIDEK ARK510A (NIDEK CO. LTD., Japan) 1–2 weeks before surgery. Children aged younger than 10 years were subjected to cycloplegic refraction by instillation of 1% cyclopentolate. Slit lamp, fundus examination, and measurement of deviation by the Krimsky method, modified Krimsky, and the alternate prism cover test at distance and near with and without glasses were performed.
All corneal topography measurements were performed using Optikon (2000) (Italy). Only the steep and flat keratometric readings in the central 3 mm zone of the anterior corneal surface were recorded.
A total of 31 eyes were included in the study. They were classified into two groups according to the type of squint surgery.
- Group A included nine patients (nine eyes) who were subjected to combined lateral rectus muscle recession and medial rectus resection in the same eye (R&R).
- Group B included 11 patients (22 eyes) who were subjected to bilateral lateral rectus recession (BLR).
All operations were performed under general anesthesia by DR Hanan using the same surgical technique, which included limbal incision conventional recession or resection. Muscles were sutured with 6-0 vicryl and conjunctiva with 8-0 vicryl.
Postoperative assessment of visual acuity, refraction, and keratometric readings were repeated at 1 day, 15 days, 1 month, 2 months, and 3 months. Corneal topography was repeated after 3 months.
Descriptive analysis of the results and their comparison within and between two groups were performed by one-way analysis of variance, followed by the post-hoc test (Tuckey). Levels of P less than 0.05 were considered statistically significant. All analyses were carried out using Microsoft Office Excel Worksheet and SPSS for Windows, version 12.0.1 (SPSS Inc., Chicago, Illinois, USA).
| Results|| |
The study included 20 patients (31 eyes) classified into two groups according to the type of squint surgery.
Group A (unilateral recess resect) (R&R): included nine eyes in nine patients, four (44.5%) males and five (55.5%) females. Their mean age±SD was 27±18.58 years.
Group B (BLR) included 22 eyes in 11 patients, four (36.4%) males and seven (63.6) females; their mean age±SD was 19±11.84 years.
Changes in best-corrected visual acuity
Group A: the mean preoperative BCVA±SD was 0.51±0.34. Postoperatively, the mean BCVA was 0.51±0.34 on the first day, 0.51±0.33 in the second week, 0.51±0.33 at the first month, 0.53±0.32 at the second month, and 0.53±0.32 at the third month.
Group B: the mean preoperative BCVA±SD was 0.75±0.23 postoperatively; the mean BCVA was 0.75±0.24 on the first day, 0.75±0.25 in the second week, 0.84±0.25 at the first month, 0.85±0.25 at the second month, and 0.87±0.25 at the third month. The BCVA showed better postoperative results in both groups, but the results were statistically insignificant (P>0.05) in group A and significant (P<0.05) in group B ([Table 1]).
|Table 1 Best-corrected visual acuity preoperatively and postoperatively in the two groups|
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Changes in spherical equivalent
Group A: the mean preoperative spherical equivalent (SE)±SD was −1.18±2.86. Postoperatively, the mean SE was −1.65±3.05 on the first day, −1.38±3.09 at the second week, −1.39±3.14 at the first month, −1.38±3.14 at the second month, and −1.17±2.92 at the third month.
Group B: the mean preoperative SE±SD was −1.36±5.03. Also, the postoperative mean SE was −1.43±4.86 on the first day, −1.59±5.03 at the second week, −1.55±5.05 at the first month, −1.72±5.05 at the second month, −1.39±4.74 at the third month.
The SE refraction showed no considerable clinical changes preoperatively and postoperatively in both groups, although the changes were statistically significant in the first week in group A (P=0.023, <0.05) and at the second week, first month, and second month in group B, P value less than 0.05, but these changes became statistically insignificant (P>0.05) at the third month postoperatively ([Table 2]).
Changes in K-readings
Group A: the preoperative mean K-reading±SD was 44.47±1.95. Postoperatively, the mean K-reading was 44.53±1.95 on the first day, 44.53±2 at the second week, 44.56±1.97 at the first month, 44.39±1.97 at the second month, 44.54±1.89 at the third month.
Group B: the preoperative mean K-reading±SD was 43.82±2.24. Postoperatively, the mean K-reading was 43.87±2.14 on the first day, 43.86±2.27 at the second week, 43.90±2.29 at the first month, 43.90±2.29 at the second month, and 43.77±2.20 at the third month. The K-readings (derived from autokeratometer) showed changes preoperatively and postoperatively in the two groups, but the results were statistically insignificant (P>0.05) preoperatively and all time points of recorded keratometry postoperatively ([Table 3]). This means that the two types of squint surgery did not cause clinically significant surgically induced astigmatism.
|Table 3 The keratometry preoperatively and postoperatively in the two groups|
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Changes in the topographical K-readings
Group A: the preoperative mean K-reading±SD was 44.60±1.91; 3 months postoperatively, the mean K-reading was 44.56±1.89 ([Figure 1]a and b, [Table 4]).
|Figure 1 (a) LT exotropia [45 prism diopter (PD)] with preoperative corneal topography; (b) postoperative 3 months after left (Lt) (R&R).|
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|Table 4 The topographical K-readings in the two groups preoperatively and postoperatively|
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Group B: the preoperative mean K-reading±SD was 43.87±2.17; 3 months postoperatively, the mean K-reading was 43.78±2.27. Therefore, K-readings obtained from topography showed no considerable changes preoperatively and postoperatively in the two groups and the results were statistically insignificant (P>0.05) ([Figure 2]a and b, [Table 4]). This means that the second types of squint surgery do not alter the corneal topography and do not cause clinically significant surgically induced astigmatism.
|Figure 2 (a) right (Rt) exotropia [70 prism diopter (PD)] with preoperative corneal topography; (b) postoperative 3 months after bilateral lateral rectus recession.|
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| Discussion|| |
It is known that the main aim of strabismus surgery is to regain the normal alignment of the visual axes of both eyes to restore binocular vision and eliminate or reduce diplopia. The other aims include treatment of abnormal head posture or improvement of cosmetic appearance. Changes in refractive power after ordinary strabismus surgery have been reported, but the results are debatable ,. The causes of refractive error changes after strabismus surgeries remain unclear. These are believed to be because of the effect of muscle tension on corneal power ,,,. Rectus muscle recession has been found to cause a reduction in the meridian of the recessed muscle and this decrease in tension of the recessed muscle is transmitted through the sclera to the cornea, which causes flattening of the corneal curvature . Also, pressure by edematous lid alters the corneal topography . The other non surgical causes that lead to flattening of the horizontal meridian of the cornea include diurnal variations of corneal power and intraocular pressure changes . Also, a noncorneal astigmatism may occur secondary to lenticular curvature changes resulting from segmental changes in the ciliary body circulation .
In the current study, we compared the effect of two different techniques [bilateral lateral rectus (LR) recession with medial rectus (MR) resection and LR recession in the same eye] over a follow-up period of 3 months. The BCVA showed better postoperative results in the two groups, but the results were statistically insignificant (P>0.05) preoperatively and at all time points of recorded vision postoperatively.
There was a statistically insignificant change in the SE in both groups, despite fluctuating changes during the follow-up periods, but these changes reverted to the preoperative level at the end of the third month. Our study is in agreement with that of Denis et al. , who reported an insignificant difference in SE after medial rectus recession in esotropia within 2–3 months.
Bagheri et al.  reported that there were no significant changes in the SE after maximum recession of four horizontal recti in patients with nystagmus.
Also, our study was in agreement with Mun et al. , who reported no change in SE after horizontal rectus muscle surgery in intermittent exotropia.
Also, our study is in agreement with Mamman and Nair , who found that SE showed a change in the myopic trend in both the groups, which was the maximum in the first postoperative week. The changes remained at 12 weeks postoperatively in both the groups, having stabilized by about 4–6 weeks, and the difference from the preoperative values were not statistically significant in both the groups.
El-Zawahry  reported that significant myopic shift and astigmatic changes in the SE refraction in the early postoperative period (3 months) after bilateral medial rectus muscle recession surgery in congenital esotropia; however, these changes disappeared in the long term (at the postoperative first year).
Our study found a statistically insignificant change in astigmatism compared with the preoperative astigmatism until the third month of the follow-up in both groups.
Our results are in agreement with those of Schworm et al. , who reported that corneal astigmatic changes after strabismus surgery were mostly small and transient.
Many researchers observed transient changes in with-the-rule astigmatism following horizontal rectus muscle surgery, but these studies found the mean change in astigmatism by evaluating corneal astigmatic changes using a keratometer or corneal topography ,.
Our results are in partial agreement with those of Al-Tamimi et al. , who observed that surgery on the horizontal rectus muscles induced statistically significant changes in the SE with myopic shift, but this change was transient and clinically insignificant. Their findings did not strongly support that there were astigmatism-induced changes. Our study is in agreement with theirs as there was no correlation between the amount of recession and/or resection and the amount of induced refractive error.
Our studies are not in agreement with Hong and Kang , who found a statistically significant persistent change in astigmatism and myopic shift in SE after horizontal rectus muscle surgery in intermittent exotropic children and recommended checking of postoperative refraction at least 3 months after surgery.
Our findings were in agreement with previous reports that showed no significant differences in induced astigmatism between the two procedures (bilateral LR recession procedure and MR resection with LR recession in the same eye) , but were not in agreement with Mamman and Nair , who found that the changes in the refractive status that occurred when two muscles are encountered in the same eye showed more change in refractive status than when only one muscle was encountered; this was also statistically analyzed using a paired t-test and found to be significant.
In our study, the K-readings (derived from topography and automated referactometer) showed no statistically considerable changes between preoperative and postoperative readings in both groups. This means that the two types of squint surgery do not alter either the corneal topography or surgically induced astigmatism.Kwitko et al.  suggested that corneal topography is affected by extraocular muscle tension and showed that recession of an extraocular muscle in rabbits caused corneal flattening in the quadrant of the recessed muscle.
Our study is in partial agreement with the Rajavi et al.  study that evaluated refractive error changes following horizontal muscle recessions, and found statistically significant differences in some aspects; however, these differences did not seem to be important clinically.
Also, our study is in agreement with the Kim et al.  study, which concluded that postoperative corneal keratometry and anterior chamber volumes did not change significantly compared with preoperative values in intermittent exotropia after performing lateral rectus muscle recession. However, the higher the ocular muscle tension, the greater were the changes in corneal astigmatism and anterior volumes.
Our studies are not in agreement with those of Mezad-Koursh et al. , who reported that with-the-rule astigmatism and myopic shift are significant complications of strabismus surgery in adults and these changes were clinically significant in 50% of the patients and recommended repeat postoperative refraction.
Rarely, the change in refractive error can be quite large and, more importantly, may result in a significant decrease in uncorrected vision. Some of these discrepancies in these studies may be caused by methodological difficulties in representing refractive power changes . Our study proved that there were no significant refractive changes after squint surgery with either a unilateral recess–resect procedure or bilateral LR recession over a follow-up period of 3 months. In conclusion, we do not recommend early cycloplegic refraction after horizontal muscle surgery to identify any surgically induced refractive changes. However, it is clear that a cycloplegic refraction is required in all cases no later than 3 months after surgery.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4]